The cuticle *The cuticle layer resembles how roofing shingles protect a house, laying over each other in layers it protects the inside the hair. Also it can open and close, depending what its pH level is...

The medulla* The middle, where all the action takes place, in hair it’s where the different chemical bonds hold fiber, proteins, melanin, and keratin together and make hair work the way it does.The cortex * The core, it’s pretty much empty space in hair where the nutrients start from in the house it’s the living space

pH stands for power + H (symbol for hydrogen)
: a measure of acidity and alkalinity of a solution that is a number on a scale on which a value of 7 represents neutrality and lower numbers indicate increasing acidity and higher numbers increasing alkalinity and on which each unit of change represents a tenfold change in acidity or alkalinity and that is the negative logarithm of the effective hydrogen-ion concentration or hydrogen-ion activity in gram equivalents per liter of the solution; also: the condition represented by a pH number.

The pH of your hair normally can range from 4.5 to 5.5. Water has a pH of 7. So there are two statements that can be said of these facts, 1, your hair is slightly acidic, and two, water is alkaline to your hair.
Anything slightly more alkaline than your hair (just over 5.5) will open your cuticle layer allowing the hair to ‘breathe’ and cause the medulla exposure. Slightly acidic to your hair (just under 4.5) will cause your cuticle layer to close down tighter.